In transmission of a video signal, it is conventional to compress the amount of transmission data in comparison with the amount of original data. An exemplary conventional method for such performing such compression is a subsampling technique which reduces a sampling frequency by thinning out the individual pixel samples of a digitized original video signal at predetermined intervals. More specifically, as disclosed in Japanese Patent Laid-open No. 57 (1982)-78290, the individual pixel samples of the video signal are so thinned out that the sampling rate is reduced by one-half, and the data of the non-thinned pixel samples are transmitted while a flag indicating the position of the non-thinned sample to be used for interpolation on the receiving side is also transmitted with regard to the thinned sample.
One problem with such a conventional subsampling process in which the subsampling pattern is not changed, is that, in the contour or the like of a subject image including high frequency components, the reproduced image exhibits conspicuous quality deterioration. Particularly when the subsampling rate is lowered, such image quality deterioration is extremely great.
For the purpose of solving the problems mentioned, the present applicant previously proposed an improved method which divides the image of one frame into a plurality of segmental blocks then selects a suitable one out of a plurality of prepared sampling patterns, and transmits, together with the pixel sample to be transmitted, an identification code representing the selected sampling pattern.
However, in this method, the number of kinds of prepared sampling patterns must be limited for suppressing the redundancy derived from the identification code, and consequently the method is not suitable for processing every image. Moreover this method has the disadvantage that the segmentation operation may bring about block distortion.